Observations of p-mode absorption in active regions

Abstract

We present here a summary of results on the interaction of p-modes with solar active regions based on observations made at the Kitt Peak Solar Vacuum Telescope and the geographic South Pole. A travelling wave decomposition of p-modes is performed in a cylindrical coordinate system centered on the active regions. Significant absorption of p-mode wave power is observed to occur in all of the regions and is a function of horizontal wavenumber (κ) - increasing linearly with k up to some maximum value and remaining constant for higher wavenumbers. The maximum fractional absorption of incident power is about 0.2 for small pores and 0.4 for typical isolated sunspots (radius = 15 Mm). A maximum of 70% absorption is seen in the large sunspot group of March 1989 (radius = 60 Mm). No convincing variation of the absorption with temporal frequency (i.e. radial order) is seen, although not entirely ruled out considering the relative errors involved with the power measurements. No significant difference in the amount of p-mode absorption is detected between equal 3-hour time intervals before and after a class X4 flare in the March 1989 region. No excess of outgoing waves following the time of the flare is detected. These observations do not support the suggestion that large flares may excite observable acoustic waves in the photosphere.